Have never understood how people can pretend being some hardcore headphone dBu-Hz -audiophiles, but still happily listening skull soundproofed from middle to two deaf halves...

Crossfeed is a mandatory feature in natural headphone listening. To put it short, it removes "virtual earplugs" from listeners ears or "soundproofed wall" between them. Without crossfeed it´s possible to hear BASS FROM OTHER EAR ONLY. Which is the one of the most unnatural things to be encountered in world of audio. Other audio tech nerd features won´t mean shit if this core-level acousto-physical basic anomaly is not properly addressed.

I personally won´t put headphones on my head without crossfeed, have come allergic for infinite channel separated bare stereo on headphones. Got kinda listening hangover from it in <1 minute. Before founding crossfeed I considered headphones for autistic rubberheads or little kids only -listening form. That changed when I undertood how human hearing works, or doesn´t work in this case, and how crossfeed could fix it.

ADI´s crossfeed 3 is still quite mild setting, "earplugs" stay still on by certain degree i.e. signal has that "wide" ping-pong -headphone stereo effect remaining. By putting it directly to 5, enables the most natural headphone listening experience ADI-2 can offer.

I don´t have anything against soundproof-feed -listeners. Just their unnatural listening habits. While preaching traditional SNR/dBu/Hz -audio gospel elsewhere.

To be clear, if this is not clear for everybody already, crossfeed is for headphone listening only. Do not use it for speaker listening.

Crossfeed has strong physiological base, but of course audiophile manners and traditions stick hard.
Many seem to think it as some kind of optional gimmick only, which doesn´t matter. Or is matter of taste at highest. This definitely is not the case: crossfeed fixes one major, core-level retardness of headphone listening, generally for all homo sapiens -branded listeners. Regardless of taste.

Think how you could hear things from speakers or live when adjusting it. Quite a reduction to headphones (infinite) channel separation is needed to achieve it, natural "channel separation" of human ears is such a small.

But... if tradition & common herd-practice requires that old-school channel selective semi-soundproof -sound while on phones, be my quest. ADI-2 has tool to fix it, if you will, though. One must only dare to flush that audiophile tradition of ping-pong -headphone sound down to toilet and begin using it.

P.S. ADI´s DSP-based crossfeed is very good. Not a sign of those old analog RC-circuit CF´s random fluctuations etc. artifacts. Settings 1-4 are too mild (still ping-pongy) in my opinion, so far only 5 is OK.

@FH1504: All your settings check out in my book. Except, turn crossfeed OFF for now. Get to know your box from this basic state and from there you can start to apply effects and EQ. Apply lightly and not everything at once. This is the best advice I can give as to sort out and apply your settings to your PERSONAL taste. Not everybody here understands that concept "personal taste" like there is some universal law for what to prefere. Although I would lean to agree with mr Kais about crossfeed.

DIM attenuates the sound by -20db.

Auto ref level will automatically go from lo- to hi-power when you crank up the volume. It works almost linear and the relais are clicking, but all in all its a pretty genius system.

Good luck on your purchase. ADI-2 DAC/PRO is great fun and a learning experience in itself. With this level of control, audio is finally "Back to the future" again.

Thanx for hinting me on my typo, as recording engineer that was a Freudian slip that I correct in my posting.

Else:
What I describe is my personal listening experience, not from a theoretical approach.
This cannot be discussed away, specially as you don’t know nothing about my listening setups (home, studio), and it’s my own personal reception of crossfeed anyway.

As they say:
Your milage may vary, and you clearly stated the fact that your’s does.
Let everyone else decide by his own, listening is the key.

As busy recording engineer I have the best ever reference for sound, the real acoustic sound of real instruments and vocal, most days in my life.

So, I’ve never asked for headphones to sound like speakers.
I just take both as what they are:
Projectors to create a nice photograph of the original, not more.

Because that’s what a recorded acoustic sound is, it can approach the original in some aspects, but never represent all it’s facets.
And then there is sound that is created during a studio production, that doesn’t even exist before being recorded and mixed.

We put a lot of effort into producing the best possible quality, and I ask speakers and headphones to preserve and reproduce as much as possible from that quality.

That’s my point:
For me crossfeed audibly degrades the quality of a recording in the mentioned ways, and I stand with what I said.

Only possibility of recording to get some advantage of switching crossfeed off from headphone signal chain, is if it´s already crossfed in recording phase. Some rare, weird "audiophile recordings" could be this kind, so called binaural recordings.

Spatial distortion of bare hp-stereo is too little known among audio folks; it has been there ever since headphones have existed and people are so accustomed to it. "This has always been this way". This thread is good example of it...

Luckily though, ADI-2 -users don´t have to follow this stone-aged hilbilly tradition, because we have ADI-2´s great Spatial Distortion Removal Tool on our free disposal. What a waste would it be to leave it off and listen on semi-deaf -mode...

Personal preference i.e. "because audio is invisible, all solutions are right" is the oldest escape of audio folks to do weird audio-things, without being busted... Crossfeed´s case this ain´t in effect though, because human physiology has so strong argument on behalf of it.

Good advice in general, but in world of audio that has high risk of leading eventually to listening WC-door handles, LEGO-block isolators and USB-cable differences. Some straight guidance is sometimes beneficial. Like now, regarding crossfeed. Hence crossfeed usage can be recommended, generally & automatically, for all headphone users! ESPECIALLY for state of the art -DSP-crossfeed -equipped ADI-2 users.

ADI-2 headphone users: ATTENTION! Present – crossfeed! Crossfeeds on 5, BOTH EARS OPEN. At ease.

Thank you all for your advice.

When Auto Reference Level is “ON”, it controls headphone out‘s Hi/Lo Power setting (and the Line Out’s reference levels).

Therefore these settings are greyed out in the menu then.

Huh? Loudness functions have their roots in psycho-acoustics and are an established, proven thing. For someone raving on about crossfeed so much, it's pretty weird to then dismiss/question loudness like this.

I don't quite have the same view as MstrC-117.

I sometimes enjoy listening with high volumes. It's the same amazing experience as in concert halls.
But most times, I use fairly low volume, even with headphones --- don't want to feel fatigue, also don't want to impair my hearing too quickly.
In this case, Loudness is a fairly useful feature.
If you always listen at high levels, loudness is not for you. But for many of us, it's essential.

The problem with loudness, however, is track must be applied with ReplayGain. Luckily it's not hard to do so.
Also for some type of music (classical) with high dynamics it doesn't work really well when the music is super quiet.
So you have to adjust the levels independently for those tracks.

Nothing wrong at listening low volume. BUT... tweaking audio band extremes when doing so definitely is wrong, and as unprofessional/un-Hi-Fi activity as can be (note: we are on pro forum now). In such a case can´t avoid thinking that an actual amateur, a bare layman, has gained acces to play on high end audio gear...

Loudness is kind of acoustical binocular/magnification glass. On that same logic´s visual version you should use binoculars strapped permanently to your head when going outdoors,  because "doing so I see distant things closer" and "binoculars are established, proven thing".

To hear bass properly, there must be volume. To see objects properly from 100 meters they must be either quite big or go closer looking. Features of human physiology and laws of physics... Sorry boys, but can´t take you confessed "acoustical-binocular" -listeners seriously after these revelations...

No. It´s question about to hear whole audio band in proper proportions to each other, in given general volume level. It´s not right to hear bass relatively much louder than midrange, what using loudness does. That´s pure form of distortion. If we are talking about Hi-Fi / naturality -wise, of course.   

Crossfade may be, crossfeed definitely is not (except rare special recordings). A recording can´t be crossfed properly in production if it´s ever intended to be used for loudspeakers. Please clarify yourself what it does to signal... 

Crossfeed may not suit optimally for certain phases in recording workflow, that I can admit. But listening the actual finished end product, which I´m writing about here, it suits 100%.

Hope you don´t mix crossfade and crossfeed in your productions like you do here... may yield weird results... could also explain your bad experiences about crossfeed...

Where does this 80 dB SPL come from? From my knowledge music productions do not have clear standards for production volumes at all. They are made on whatever SPL/deafness-level Pro Tools -artist etc. DJ in charge has.

Lot of excuses could be made for justifying "acoustical-binocular" -listening. Depends on listeners Lo-Fi -tier, attitude and knowledge. Some listeners may use wunderbaums and even dig their nose during listening, because "that feels good" also.

Again, it´s question about to hear whole audio band in proper proportions to each other.  Using loudness to distorting that balance/proportions is like using ladies ass narrowing mirror or walking outdoors binoculars on head (visual versions of loudness).   

Bad headphones/loudspeakers are subject of their own, acoustical responses must be as flat as possible.

Harman Target -curve is nothing else but "most pleasing" -election winner of bunch of amateurs. It´s already changed several times. Real headphone listeners don´t use Harman curves for their phones for sure.

I like eggs, any form of of eggs cooked as long as it is not an bad egg.

On vacations overseas, at some hotels, they offer boiled eggs at breakfast, some boiled for 3 mins, some 5, also pan fried eggs, sunny side up, both sides fried, you name it.

In Portugal, it is not allowed to serve eggs not completely cooked, you still can ask for an egg with running yolk, but the cook will not take any responsibility if something goes wrong after you ate it.

Loudness, EQ and B/T are function(s), use it when needed, if you do not like it, disable it.

It is about the choice, available choice, to compensate individuals, could be the music, could be the amp type, could be the speaker type, could be the room acoustics and human ears as well. Vinyl and CD or a radio broadcast and streaming is a fixed thing from production, it cannot be change after it was produced, though you can blame the producer, the function(s) at a piece of equipment allows you to alter something according to someone's need. There is no fixed rule for such adjustment, it is personal taste.

People can walk outside when raining without a raincoat or umbrella, human skin is waterproof, and it doesn't hurt others, right?

Eat raw or or cooked, seasoning it with pepper, salt, sugar, spices or do nothing is a choice, to each his own, period.

@ MstrC-117

I give you first hand information from a highly skilled and knowledgeable studio owner, audio engineer and producer - me.

Not a DJ or artist doing more or less advanced homerecording.
Decades of personal experience, no internet hearsay.

Hope you will stop to ignore and neglect this information and stop repeating your same, wrong points over and over again.
Start to listen, please.

You asked, and so I just further explain one point, even for those reading along.

How is superior studio quality crossfeed for headphones already integrated into commercial recordings?

Headphones playback has been taken into consideration when recording and mixing for a long time.
Since the 70s a lot of developments in recording technology are based on head related principles.
Engineer do compatibility checks for headphones playback during production.

It starts with main microphones selection and placements like:

The fully head related ORTF microphones arrangement, that uses human’s ears distance for the main stereo mic pair, works angle-correct on headphones.

Same for the OSS mic. It uses a special head sized disc between a stereo pair of mic’s, much like a dummyhead recording, but without it’s downside of strange coloration.

These are fully compatible to headphones, have a natural crossfeed per design.

Decca tree, widely used for classical recordings, is a wider spaced stereo pair of mic’s, but has an additional center “mono“ mic that‘s feed to both ears = full natural acoustical crossfeed that does NOT compromise the signal quality like later DSP processing.

There are numerous other main mic placements like NOS or DIN, non of which separates left/right more than the human auditorial system.
All tend to already narrow the stereo base at lower frequencies, comparable to the human ears.

Additionally to the main mic, the engineer places spot mic’s (to feature certain instruments).
Their signal doesn’t go just full left or right, but is panned, “crossfeed” into the stereo positions that are already projected and defined by the, see above, head related main mic’s.
As these spot mic’s are (opposed to the main mic’s) fully phase-coherent, they would be unnaturally boosted up to 6 dB by later crossfeed.

Room mic’s and/or additional electronic reverb is added, to capture the real ambience and/or enhance or create an appropriate room definition and soundfield.
These are very vulnerable for later stereo signal manipulation like post-crossfeed, as they contain a lot of left/right antiphase signal that is canceled out by crossfeed.
Crossfeed indeed tends to knock those off the table, although they are an important part of the artistic decisions.
Same, BTW, applies to the ambience information from the main mic’s.

Conclusion:
ADI-2’s (and other’s) Crossfeed Function narrows the stereo field in a way NOT intended by the production team, selectively reduces certain signals, boosts others.

This is the opposite of “natural” by your own definition of reproducing the recorded signal as faithful as possible.

DSP based crossfeed on a readily mixed stereo signal is a sound effect, you might like it or not, but that’s all about it, nothing more.

If you now find some typos, you can keep them and I won’t pay you for lecturing my postings.

Dear highly skilled and knowledgeable studio owner, audio engineer and producer. Despite your apparent knowledge of microphone techniques, you don´t seem to understand the actual core problem here.   
How recording can be "optimized" simultaneously for loudspeaker and headphone playback, when loudspeakers have acoustical channel separation only head-shadowing-effect -much (very little) and headphones have it skull-splitted-to-half -much (infinite separation/soundproof between ears)?

Those "natural crossfeed" including mic-techniques you describe, are used mostly in weird and rare áuteur-music-productions. They may benefit crossfeed less than typical 2ch -material, but as a penalty shot their performance in speaker playback is somewhat compromised. You are some kind of árt déco / "alternative" music -producer?

Your earlier bragged comparations of (probably just not enough) crossfed headphone playback and your 30k€ speaker system is also pretty ridiculous to begin with, like comparing Volkswagen Golf vs. Leopard 2 off-road abilities. Crossfeed should be compared against the same headphones, just without crossfeed. In this threads case 300€ Sennheiser HD 600, ADI-2´s Crossfeed OFF / Crossfeed 5.

Well, thank you for all this information.
I believe it is time to end the conversation that drifts away from my initial question.

RECORDING CAN´T BE DONE TO BE OPTIMAL SAME TIME FOR HEADPHONES AND LOUDSPEAKERS. You don´t seem to undestand, or are pretending not to understand, loudspeakers and headphones vastly differing acousto-physical decoupling mechanisms. Or maybe your understanding of concepts "natural", "spatially correct" and "right sounding" is just... too distort... eeh... "personal".

Commercial emphasis on vast majority of recordings has been on loudspeakers. Your headphone-stereo friendly stereo-mic -recordings are in real world rare, commercially available from weird boutique-channels only. Maybe you sell this kind of marginal stuff yourself? From your garage maybe? If one himself is deep enough in the marginal, doesn´t necessarily realize how things actually are in general, outside that esoteric -bubble.
And when we exit from stereo -world, into realm of downmixed multichannel (TV, movie, game) sound on headphones, already high need of proper crossfeed solution blows straight out of the roof.

I can tell you right now. Crossfeed at 5 = best way to cramp any soundstage. If you say its a matter of taste I totally and 100% agree with you. If you say everybody must use high crossfeed settings to get the "right" sound, you dont even want to know what I mean. IMHO youre telling everybody to get the wrong sound, but thats just me. One more thing. Whitout taking any away from its founders, I think, RME forum is more for tech support and such. Not really a debate fora. Maybe you could take this noise elsewhere. Given the intensity of your argumentaion, someone professional perhaps!?

As nice as the idea of crossfeed may be in principle. I also took the challenge/effort (again, after long time) to find out whether crossfeed enriches the sound over headphones for me or not.

The first thing that bothers me is that the sound image is suddenly no longer coherent. Something seems to be out of balance. I can't describe it at the moment better than saying, I was missing something in the treble range.

Then I also had to realize that it depends on the audio material whether crossfeed can be used at all at level 5 and to sound still reasonably/coherent. Some things only sounded better again when crossfeed was turned down to level 2.

My conclusion: it did not convince me. Also not the suggested approach to listen to it on level 5 for a week.
Ears get used to sound quickly, which is why mastering engineers change audio material more often or take breaks to listen to something with fresh ears. In this respect, I think it's a completely wrong recommendation to "force" yourself to listen to it for a week in order to like it. Listen with fresh ears and either you like it or not.

But everybody is free to use the features as he want, I only describe my discoveries / taste, I have no intention to tell other people whether or how they ought to use crossfeed.

@Happy_amateur: thank you for your remark, I would also find it much more relaxed if such discussions in the forum would be led in a more cultivated respectful tone. This has always been something the RME forum could be proud of and where it was pleasantly different from the usual forum landscape on internet.

Or you visit a classical concert in a dedicated concert hall.

Indoor live Classical is without amplification through microphones or speakers in general, purely acoustic.

Even if you‘re not into this music style, I suggest to audition such an event at least once in your lifetime.
Listening to a live Symphonic Orchestra can be an overwhelming experience.

Couple additional remarks regarding crossfeed

1) If a recording is meant to be working with loudspeakers, crossfeed improves it for headphone listening. Thats the acousto-physical fact. You may not like the results, but bare fact remains. Period.

2) Recording which is not meant to work with loudspeakers, won´t work with crossfeed. Hence testing crossfeed with headphones designed, most rare, esoteric & weirdest stereo-pair -jazz -recordings gives totally distorted picture of its capabilities.

3) Crossfeeds purpose is to sound right. Sounding right does not always mean  sounding pleasing/good. Proper crossfeed reveals mercilessly what an garbage some recordings are. Removing ping-pong -headphone stereo effects, to which listener is fully accustomed, may first seem soundstage shrinking/uncoherence. Patience... mind needs to recalibrate into new right sound. Same shock as a baby (or later) you were weaned from dummy... 
Adjusting crossfeed for individual recordings is same as adjusting bass, midrange and treble i.e. EQ in same situation: utter please-me-don´t-tease-me -Lo-Fi-pleasing behavior. Be a man, accept the truth and deal with it (skip next piece). Real men do not need constant pleasing/ear licking/dummy in their listening!

4) If one has listened headphones tens of years in soundproof-feed -mode, it would be unreasonable to expect change to happen snap-like-that -manner. Hence longer testing period. One week should be realistic rehabilitation schedule for even more exposed headphone abusers to get their shit together.

5) Everyone in this forum has the same ADI-2 -device and crossfeed. Hence this is perfect place to discuss crossfeed, among other RME-things!

I used crossfeed 5 for my HD800 for quite a while and really liked how it changed the presentation. But nowadays I've found a great middle-ground with crossfeed 2; it still retains great imaging but still makes it so any hard-panned sound isn't weird to my ear, after going more into speakers and getting used to the more natural presentation.

Really love having the option, and since I can just toggle it on and off from my sofa via the remote, it's easy to quickly test a song if it sounds better or worse for me with crossfeed on or off.